OS：Red Hat Enterprise Linux Server release 6.5 (Santiago)
Questions：I use pt-online-schema-change to cause the mysqld service to restart when adding an index in a table with 50 million records.
pt-online-schema-change runs regular queries (in a complex sequence, I know) so it shouldn’t cause MySQL to crash.
From the attached error log I see this:
019-03-28T08:09:24.905320Z 0 [ERROR] Function 'validate_password' already exists
2019-03-28T08:09:24.905374Z 0 [ERROR] Couldn't load plugin named 'validate_password' with soname 'validate_password.so'.
2019-03-28T08:09:24.925899Z 0 [ERROR] Function 'validate_password' already exists
2019-03-28T08:09:24.925967Z 0 [Warning] Couldn't load plugin named 'validate_password' with soname 'validate_password.so'.
2019-03-28T08:09:24.926381Z 0 [Warning] Plugin validate_password reported: 'Dictionary file not specified'
and more: at the beginning of the error log it says signal 11. That’s a MySQL internal error.
08:07:45 UTC - mysqld got signal 11 ;
I only saw a similar error on MySQL 8 having empty users and roles and that was causing a different program (minimum_permissions) to fail after MySQL crashed with a signal 11.
Could you verify that there are no invalid/empty users in your db?